The invention relates to a radiation image taking apparatus to be used in a medical field, industrial field and the like, and more particularly, it relates to a technique for removing moires generated on an output screen when the detected results are outputted.
A conventional radiation image taking apparatus includes a grid provided with a number of slits on an entering side of radiations of a radiation detection pixel matrix to remove dispersion rays contained in X-rays passing through a sample to be measured.
When X-rays passing through the sample to be measured pass through the grid, since the dispersion rays are shut off by the grid, it is possible to prevent an image quality from being lowered by the dispersion rays. However, in case there are gaps of pitches between the slits provided on the grid and the detection pixels, respectively, irregularities in the detected radiation signals are generated to thereby generate moires on a screen of an image displaying device. In such a case, the following methods have been taken.
As a fist method, a grid is formed accurately such that pitches of the slits disposed on the grid are the same as those in the radiation detection pixel matrix, and the grid is located close to the radiation detection pixel matrix or integrally formed therewith.
As a second method, a grid is positioned close to a one-dimensional or two-dimensional radiation detection pixel matrix, and is horizontally swung or moved in a pitch direction of the grid with respect to the radiation detection pixel matrix so that projection images projected through the grid are uniformly projected to the respective positions on the radiation detection pixel matrix.
Further, as a third method, when a motion image is taken, prior to a measurement, levels of the radiation detection signals of the respective detection pixels are measured beforehand, and a position of the grid is set so that the detecting levels of the respective detection pixels become substantially uniform. In other words, if necessary, the grid is fixed with a proper inclination angle with respect to the radiation detection pixel matrix.
However, the conventional radiation image taking apparatus having the structure as described above has the following problems.
In the first method where the grid having the high pitch accuracy is disposed close to the radiation detection pixel matrix or integrally formed therewith, it is extremely difficult to accurately form the pitches of the slits formed on the grid. Therefore, in case there is a fine error in the pitch accuracy of the manufactured grid, as shown in FIG. 7, toward a pitch direction of the grid, i.e. plus direction on an X-axis in the drawing, the detection pixels and slit positions of the grid do not match their positions gradually. In other words, in an area A in FIG. 7, since there is no gap between the slit of the grid and the detection pixel, an X-ray detecting signal (+)1 is detected from the detection pixel. However, as it comes to the pitch direction of the grid, due to the gaps between the slit disposed on the grid and the detection pixel, the X-ray detection signals detected from the detection pixel become zero (0) in an area B and (xe2x88x92)1 in an area C. As apparent from the above, the level changes of the X-ray detecting signals detected at the detection pixels are repeated according to the gaps of the positions of the slits on the grid and positions of the detection pixels. As a result, as shown in FIG. 8, there arises a problem where the gaps appear as moires on a displaying screen.
In the second method where the grid is swung or moved, when a moving image is taken, the swinging or movement of the grid must correspond to an image taking mode of 30 frames/second to obtain a smooth moving image. That is, a high speed swinging unit of one several millionths in a second is required in order that the swinging of the grid corresponds to the image-taking mode. Therefore, it is very difficult to remove moires by the movement when the moving image is taken. Also, since a large apparatus is necessary to swing or move the grid, there is a problem of obtaining an installation place of the apparatus and an economical burden.
In the third method, the radiation detecting signals of the respective radiation detection pixels disposed in a matrix shape are measured beforehand and the grid has to be set at a position where the radiation detection signals of the respective pixels become uniform, which results in an operational burden to an operator. Also, since it is necessary that the grid is positioned with a three dimensional inclination in horizontal and vertical directions with respect to the radiation detection pixel matrix, a larger apparatus is required, which is uneconomical.
In view of the above defects, an object of the present invention is to provide a radiation image taking apparatus for removing moires from a detected image without using a grid with high accuracy.
Further objects and advantages of the invention will be apparent from the following description of the invention. Summary of the Invention
The present invention has the following structure in order to attain the above-stated object.
A radiation image taking apparatus according to a first aspect of the invention includes a radiation irradiation device for irradiating radiations to a sample to be measured; a grid having a number of slits for allowing the radiations to pass therethrough to remove dispersion rays from the radiations passed through the sample to be measured; a radiation detecting device wherein detection pixels for detecting radiations passing through the grid are arranged in a one-dimensional or two-dimensional matrix shape; and an image output device for outputting a detected image. In the invention, pitches of the slits of the grid are set to have such a relationship that when X-rays are projected to the radiation detecting device through the grid, a length obtained by multiplying odd-number to a half pitch of the projection image on the radiation detecting device through the grid is equal to a pitch of detection pixels of the radiation detecting device; and there is provided an operation device where the radiation detection signals obtained from the radiation detecting device are subjected to an equalizing process for every pixel groups, each having an even number of detection pixels continuously lined up in a pitch direction of the grid, and are provided to the image output device.
In a radiation image taking apparatus of the second aspect, in the radiation image taking apparatus of the first aspect, the pitches of the grid are set to have such a relationship that when radiations are projected to the radiation detecting device through the grid, a half length of the pitch of the projection image is equal to a pitch of a detection pixel of the radiation detecting device; and there is provided an operation device wherein the radiation detection signals obtained from the radiation detecting device are subjected to an equalizing process for every two detection pixel groups continuously lined up in the pitch direction of the grid, and are provided to the image output device.
A radiation image taking apparatus of the third aspect further includes, in the radiation image taking apparatus of the first aspect, a swinging or moving device for swinging the grid in a pitch direction; and a switching device for swinging the grid when a stationary image is taken, and for fixing the grid by stopping the swinging device when a moving image is taken.
The radiation image taking apparatus of the invention operates as follows.
According to the first aspect of the invention, the grid provided to the radiation image taking apparatus has a pitch of slits such that when radiations irradiated to the sample to be measured from the radiation irradiation device are projected to the radiation detecting device through the grid, a length obtained by multiplying odd-number to a half pitch of the projection image becomes equal to a pitch of detection pixels of the radiation detecting device. Then, the radiation detection signals detected at the radiation detecting device through the grid are subjected to an equalizing process for every pixel units, each having an even number detection pixels continuously lined up in a pitch direction of the grid. That is, since the equalizing operation process is carried out with a combination, as a unit, of a high level radiation detection signal and a low level radiation detection signal from the radiation detection signals detected by the radiation detecting device, irregularity levels of the radiation detection signals can be canceled, i.e. equalized. As a result, it is possible to remove moires from an output image outputted from the image output device.
According to the second aspect of the invention, the grid used in the radiation image taking apparatus according to the first aspect is set to have a relationship such that a length of a half pitch of a projection image is equal to a pitch of a detection pixel of the radiation detecting device. Then, the radiation detection signals detected from the radiation detecting device through the grid are inputted into the operation device and subjected to an equalizing process for every two detection pixels continuously lined up in a pitch direction of the grid. That is, through the operation process for equalization by using the radiation detection signals of a two-pixel unit, a decrease in resolution can be limited to the minimum rather than equalization by using the radiation detection signals with an even-number unit more than 4 pixels.
According to the third aspect of the invention, when a stationary image is taken, the grid is swung or moved in the pitch direction with respect to the radiation detecting device. In other words, the projection image projected on the detection pixels of the radiation detecting device through the grid is made uniform, so that the radiation detection signals detected from the radiation detecting device become uniform to thereby remove moires from the output image outputted from the image output device. That is, since it is not necessary to correct the image by the operation process, an output image having a high resolution can be obtained by reducing deterioration of the output image. Also, when a moving image is taken, moires can be removed from the output image by stopping swinging of the grid through a switching device and using an operation device and the grid according to the first or second aspect.